In Januari 2016 I visited the Opening Ceremony of this spectacular festival in Harbin, northeast China, for two days. The temperature was -28 degrees Celsius!
I found this interesting documentary by Dominic Swire, who investigated the role of immigrant workers. It gives a quite complete view on the construction process, and the large amount of work involved in this spectacular, and economically important, event.
Source: https://www.youtube.com/watch?v=C2szFIdqV3M